Reliability Analysis of Structures with Multiple Site Fatigue Cracks

1.基于多点疲劳裂纹无损检测的可靠性分析讨论了不可避免的不确定参数对检测规划的影响。与检验规划相关的不确定性可分为两类：工程不确定性和经济/社会不确定性。通过检查结果和/或服务体验进行更新，可以逐渐减少初始不确定性。将贝叶斯分析与序贯成本最小化方法相结合，应用于具有成员疲劳特性不确定性的成员集。材料性能分布估计及其对疲劳扩展寿命的影响用实验方法讨论了预测疲劳裂纹扩展的随机模型。该模型基于较大的紧凑拉伸试件在恒定应力强度因子范围、上填充三角形、K条件下的疲劳试验结果。主要研究结果如下：1)疲劳裂纹扩展的材料性能存在大尺度变化和小尺度变化。2)建立材料性能沿裂纹路径的统计关联模型是非常重要的，特别是当关联长度较大时。基于信息量最大化的首次检测时间选择首次检测时间对结构的整体可靠性影响很大，因此从前人的工作中可以看出几个成本因素。通过优化效用函数(这里简单地将其视为平均香农信息)，讨论了选择首次检验时间的合适准则。

1. Reliability Analysis based on Non-Destructive Inspection of Structures with Multiple Site Fatigue cracks.The influence of inevitable uncertain parameters on inspection planning was discussed. The uncertainties related to inspection planning can be classified into two categories : engineering uncertainty and economical/social uncertainty. Initial uncertainty can be gradually reduced by being updated through inspection results and/or service experience. The Baysian analysis is applied in conjunction with the sequential cost minimization method for a member set which has an uncertainty in the fatigue property of members.2. Estimation of Distribution of Material Properties and its Effect on Fatigue Propagation Life.A stochastic model for predicting fatigue crack growth was discussed by experimental approach. The model is based on the results of fatigue test using relatively large compact-tension-specimen under constant stress intensity factor range, (〕SY.upper filled triangle.〔) K, condition. The main results are : 1) There are large scale variation and small scale variation of material properties of fatigue crack growth. 2) It is very important to model the statistical correlation of material properties along crack path, particularly when the correlation length is large.3. Selection of the First Inspection Time based Maximization of Amount of Information.The first inspection time heavily infuences the overall structural reliability, and therfore several cost components as was noticed from pervious works. By optimizing an utility function, here simply regarded as mean Shannon information, a suitable criteria for selecting the first inspection time was discussed.